In the prior art, use of the expression “pixel” is known to denote the item of information, representative of a portion of the image, received from one of these detectors.
In the context of this invention, more particularly, systems known as “push-broom” systems are considered. In these systems, represented in FIG. 1, the image 101 acquired by the sensor 102 scrolls in a known direction with a known speed 103. This scrolling of the image is caused for example by the movement of the satellite. Each optical detector belongs to a column denoted by i and a row denoted by j. Due to the movement of the image, a portion of the image is viewed successively by the detectors of the same column i. A processing device provides for summing, for each column, the information received from different rows and according to a given summation time. Also known in the prior art is the use of the term “integration” for this sum. This functionality is also known as TDI (Time Delay Integration).
Optical acquisition systems are known for which the sensor uses CCD (Charge-Coupled Device) fabrication technology. However, these optical acquisition systems do not provide for varying the number of rows used for carrying out the sum as a function of the location of the column on the matrix having a TDI functionality. Furthermore, optical acquisition systems using this fabrication technology do not provide for precisely taking into account variations and distortions present in particular on the lenses placed before the optical sensor. Indeed, with this technology the number of rows summed is identical for all the columns of the matrix having a TDI functionality and does not take into account image quality variations over the length of the detectors.
Also known are optical acquisition systems for which the sensor uses CMOS (Complementary Metal Oxide Semiconductor) fabrication technology. The choosing of the summation time from an item of information representative of the luminance received by the detector of the first row is known, this being done in order to maximize the quality of the acquired image. If the information received from the detector of the first row is not representative of the information received from the other detectors of the image, the determination is hence not good for the remainder of the image. Determining the summing time in order to maximize a function made up of the pair formed by the modulation transfer function, or MTF, and by the signal-to-noise ratio, or SNR, for a given reference luminance value, is also known. The modulation transfer function, or MTF, describes the clarity of the image, and the signal-to-noise ratio describes the noise of the image. However, since this determination is factory-performed from the detector of the optical acquisition system corresponding to average or minimum image quality on the detector, the transmission from the optics, therefore the SNR and MTF, varies along the detector. This determination does not provide for adapting to variations of reception conditions.